Baking normals from high to low poly mesh for game object
It's not actually required that you unwrap the high poly mesh for this operation to work, only that the two meshes be in the same location when you do the baking. Development of aberrations around corners is a common problem with normal maps. Cycles allows baking now and has a cage function that may help. 

Take your low poly model and make a duplicate of it. This is going to be the cage object. Using Atl+S increase the size of the cage object to be slightly larger than the target object. You may have to do a little tweaking to the cage to ensure that it has an even surface around your target object

Switch to Cycles Render and create a new material for the target object.

Create a new image to act as the normal image

In the node editor go to the material for the target object and create an image texture node and load the normal image you just created into the node. The node does not have to be connected to anything it just has to be there.

Go to the Render tab in the properties window, go down to Bake, select Normal in Bake Type, set Space to Tangent, check Selected to Active and Cage, and select the cage object in the object selection window

Select the hi-res source object followed by the lo-res target object and click on the Bake button. 

If all goes well you should get a much different result than the one you're getting now.